In wireless delivery of contents such as stream delivery, a predetermined band is secured between a server that delivers the contents and a terminal that receives the contents, in, order to smoothly reproduce contents that are required to reproduce in time, such as an audio, a moving image, and the like. The contents are delivered from the server to the terminal by wireless or wire via a device such as a router. The technique of securing the band is known as a QoS (Quality of Service).
In the above technique, a band specified by a server that delivers a content is reserved between a content transmitting device and a content receiving device before the content is transmitted in order to assure a constant communication speed for transmitting the content.
Examples of the above technique of securing the band are disclosed by the following patent document 1 and patent document 2. The following simply describes each of techniques of the patent documents 1 and 2, with reference to the attached drawings.
The patent document 1 discloses a system in which an optimum settable value is set in a band setting when a content is transmitted and received. A specific example of the system is shown in FIG. 17. A content is transmitted from a content transmitting terminal 1700 to a content receiving terminal 1720 via relay devices 1710a and 1710b. The content transmitting terminal 1700 firstly reserves a band required for transmitting a content before transmitting the content. The content transmitting terminal 1700 specifies both of a requested band required for optimally transmitting the content and a minimum band required for minimally transmitting the content for the relay device 1710a. Here, the requested band is referred to as “request band”, and the minimum band is referred to as “minimum request band”. The request band indicates the highest level of the band that is considered most desirable for receiving a content, and the minimum request band indicates the lowest level of the band for managing to receive the content. In FIG. 17, suppose that a request band requested by the content transmitting terminal 1700 is 18 Mbps (Mega Bit Per Second), and a minimum request band requested by the content transmitting terminal 1700 is 12 Mbps. Then, the relay device 1710a detects an unassigned band that can be secured by the relay device 1710a. Here, suppose that the unassigned band of the relay device 1710a is 20 Mbps. Then, the relay device 1710a notifies the relay device 1710b of a band setting request indicating that the request band is 18 Mbps, and the minimum request band is 12 Mbps.
Next, suppose that an unassigned band of the relay device 1710b is 16 Mbps. Then, the relay device 1710b notifies the content receiving terminal 1720 of a band setting request indicating that the request band is 16 Mbps, and the minimum request band is 12 Mbps.
The content receiving terminal 1720 determines the band 16 Mbps that is the highest settable band at the time as a band that can be secured for receiving the content. Then, the content receiving terminal 1720 transmits a band setting response indicating 16 Mbps as the settable band information to the content transmitting terminal 1700 via each of the relay devices. As a result, the content transmitting terminal 1700 transmits the content to the content receiving terminal 172Q at a communication speed of 16 Mbps. Using the technique disclosed by the patent document 1, contents can be transmitted and received in the highest level of the band that can be secured when the band is secured.
The patent document 2 discloses the following system as shown in FIG. 18. The system includes a wireless master device 1810a and a wireless master device 1810b each of which is arranged on a wired network, a wireless slave device 1820a, a wireless slave device 1820b, and a wireless slave device 1820d each of which is wirelessly connected to the wireless master device 1810a, a wireless slave device 1820c which is wirelessly connected to the wireless master device 1810b, and a manager 1800 on the wired network to which each of the wireless master devices is connected, which manages each of the wireless slave devices is wirelessly connected to which wireless master device. The patent document 2 discloses a method to avoid a case in which a band is insufficient when data is transmitted and received, by controlling the system so that a traffic volume in each part of the network becomes even as much as possible.
In FIG. 18, three wireless slave devices are connected to the wireless master device 1810a. Also, one wireless slave device is connected to the wireless master device 1810b. In this case, the number of the connected wireless slave devices is different between the wireless master device 1810a and the wireless master device 1810b. As a result, a traffic volume in the wireless master device 1810a is larger than a traffic volume in the wireless master device 1810b. 
Therefore, when the manager 1800 that manages a traffic volume in the network detects that the traffic volume in the wireless master device 1810a exceeds a threshold value, the manager 1800 detects whether or not any of the wireless slave devices wirelessly connected to the wireless master device 1810a can be wirelessly connected to the wireless master device 1810b. When detecting that the wireless slave device 1820b can be wirelessly connected to the wireless master device 1810b, the manager 1800 instructs the wireless slave device 1820b to switch a connection destination from the wireless master device 1810a to the wireless master device 1810b. As a result, the number of the wireless slave devices connected to the wireless master device 1810a decreases and the traffic volume in the wireless master device 1810a also decreases. This can avoid a case in which communication is interrupted between the wireless slave devices connected to the wireless master device 1810a and the wireless master device 1810a. 
Patent Document 1: Japanese Published Patent Application No. H10-145424
Patent Document 2: Japanese Published Patent Application No. 2000-69050